首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   113462篇
  免费   17871篇
  国内免费   9984篇
化学   73149篇
晶体学   1318篇
力学   7558篇
综合类   536篇
数学   13109篇
物理学   45647篇
  2024年   100篇
  2023年   2110篇
  2022年   2267篇
  2021年   3341篇
  2020年   4253篇
  2019年   4132篇
  2018年   3572篇
  2017年   3280篇
  2016年   5223篇
  2015年   4859篇
  2014年   6013篇
  2013年   8073篇
  2012年   9864篇
  2011年   10577篇
  2010年   7033篇
  2009年   6748篇
  2008年   7214篇
  2007年   6695篇
  2006年   6233篇
  2005年   5180篇
  2004年   3930篇
  2003年   3036篇
  2002年   2616篇
  2001年   2615篇
  2000年   2138篇
  1999年   2353篇
  1998年   2033篇
  1997年   1920篇
  1996年   2024篇
  1995年   1670篇
  1994年   1629篇
  1993年   1297篇
  1992年   1211篇
  1991年   1123篇
  1990年   919篇
  1989年   668篇
  1988年   550篇
  1987年   456篇
  1986年   440篇
  1985年   395篇
  1984年   296篇
  1983年   190篇
  1982年   166篇
  1981年   134篇
  1980年   92篇
  1979年   59篇
  1978年   51篇
  1976年   63篇
  1975年   60篇
  1974年   64篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
71.
Journal of Thermal Analysis and Calorimetry - The fire behavior of one flame-retardant PVC cable used as building wire is investigated in this work. Bench scale tests were performed using a cone...  相似文献   
72.
73.
Monoester‐diterpenoid alkaloids are the main bioactive components of Sini decoction, which is a well‐known traditional Chinese medicine formula for the treatment of myocardial infarction (MI) and heart failure in China. In this work, an ultra‐high‐performance liquid chromatography–mass spectrometry combined with microdialysis method was successfully established and applied for investigating for the first time comparative plasma pharmacokinetics of three monoester‐diterpenoid alkaloids (benzoylmesaconitine, benzoylaconitine and benzoylhypacoitine) in normal and MI rats after oral administration of Sini decoction. The statistical results of pharmacokinetic parameters demonstrated that benzoylmesaconitine, benzoylaconitine and benzoylhypacoitine showed lower peak concentration, longer half‐life, smaller area under the concentration–time curve, slower clearance, time to peak concentration and mean residence time in MI rats than in normal rats (p < 0.05), which indicated that monoester‐diterpenoid alkaloids exhibited lower systemic exposure and slower elimination in the MI rats. The results provided the experimental basis for understanding the metabolic fate and therapeutic effects of Sini decoction.  相似文献   
74.
Acta Mathematicae Applicatae Sinica, English Series - This paper summarizes the parameter estimation of systems with set-valued signals, which can be classified to three catalogs: one-time...  相似文献   
75.
Chen  Shuang  Pang  Li-ping  Li  Dan  Wang  Jin-he 《应用数学学报(英文版)》2019,35(3):591-606
Acta Mathematicae Applicatae Sinica, English Series - For the variational inequality with symmetric cone constraints problem, we consider using the inexact modified Newton method to efficiently...  相似文献   
76.
In this paper, an unstable linear time invariant (LTI) ODE system is stabilized exponentially by the PDE compensato—a wave equation with Kelvin‐Voigt (K‐V) damping. Direct feedback connections between the ODE system and wave equation are established: The velocity of the wave equation enters the ODE through the variable vt(1,t); meanwhile, the output of the ODE is fluxed into the wave equation. It is found that the spectrum of the system operator is composed of two parts: point spectrum and continuous spectrum. The continuous spectrum consists of an isolated point , and there are two branches of asymptotic eigenvalues: the first branch approaches to , and the other branch tends to ?. It is shown that there is a sequence of generalized eigenfunctions, which forms a Riesz basis for the Hilbert state space. As a consequence, the spectrum‐determined growth condition and exponential stability of the system are concluded.  相似文献   
77.
丛玉豪  胡洋  王艳沛 《计算数学》2019,41(1):104-112
本文研究了一类含分布时滞的时滞微分系统的多步龙格-库塔方法的稳定性.基于辐角原理,本文给出了多步龙格-库塔方法弱时滞相关稳定性的充分条件,并通过数值算例验证了理论结果的有效性.  相似文献   
78.
This paper develops a framework to deal with the unconditional superclose analysis of nonlinear parabolic equation. Taking the finite element pair $Q_{11}/Q_{01} × Q_{10}$ as an example, a new mixed finite element method (FEM) is established and the $τ$ -independent superclose results of the original variable $u$ in $H^1$-norm and the flux variable $\mathop{q} \limits ^{\rightarrow}= −a(u)∇u$ in $L^2$-norm are deduced ($τ$ is the temporal partition parameter). A key to our analysis is an error splitting technique, with which the time-discrete and the spatial-discrete systems are constructed, respectively. For the first system, the boundedness of the temporal errors is obtained. For the second system, the spatial superclose results are presented unconditionally, while the previous literature always only obtain the convergent estimates or require certain time step conditions. Finally, some numerical results are provided to confirm the theoretical analysis, and show the efficiency of the proposed method.  相似文献   
79.
Xu  Wu  Zhang  Yuanya  Achi  Oliver Y.  Knierim  Kathleen D.  Hanks  Justin G.  Wang  Yingchun 《Structural chemistry》2019,30(4):1459-1470
Structural Chemistry - ERK1 is an important kinase in Ras–Raf–MEK signaling. We have recently demonstrated by mass spectrometry that Tyr210 of ERK1 can be nitrated, and the nitration...  相似文献   
80.
A polystyrene-supported phosphine oxide-catalysed Beckmann rearrangement of ketoximes in 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) has been developed. Good substrate compatibility, mild reaction conditions, good yields as well as the reusability of the catalyst/solvent made this procedure more environmentally benign.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号